#include <stdio.h>

// 元素 elem 进栈
int push(int *a, int top, int elem) 
{
    a[++top] = elem;
    return top;
}

// 元素出栈
int pop(int *a, int top)
{
    if (top == -1) {
        printf("空栈");
        return -1;
    }
    printf("弹栈元素：%d\n", a[top]);
    top--;
    return top;
}

int main()
{
    int a[100];
    int top = -1;
    top = push(a, top, 1);
    top = push(a, top, 2);
    top = push(a, top, 3);
    top = push(a, top, 4);
    top = pop(a, top);
    top = pop(a, top);
    top = pop(a, top);
    top = pop(a, top);
    return 0;
}